GNGTS 2014 - Atti del 33° Convegno Nazionale

GNGTS 2014 S essione 1.1 59 magnitudes ~6.5 are expected on the order of every hundred years and will likely provide the largest contribution at hose return period. Events with magnitudes beyond the currently accepted M max 6.7 (return period > 1000 years) will progressively provide decreasing contributions to predicted peak ground motions and will mainly affect the design of such buildings required to sustain shaking levels at return period > 500 years. Conclusion. The comparison between geodetically estimated moment accumulation rate and that released seismically by the earthquakes in the past 1000 years suggests that to balance the observed rate of strain accumulation a large part of the observed interseismic coupling is released aseismically or by the occurrence of infrequent large ( M > 7) earthquakes with very long return period (> 1000 years), and with a moment magnitude larger than the maximum magnitude ( M W 6.7) value assigned to the largest expected event in the area in most seismic hazard estimates. In conclusion, we therefore suggest that the occurrence of a M ~7.5 earthquake cannot be reasonably excluded, if different segments of the southern front of the eastern Alps would break simultaneously. The large uncertainties on maximum magnitude and fraction of aseismic deformation require however additional seismological and geological investigations to understand the hazards posed by active faults along the Alps thrust belt. References Anselmi M., Govoni A., De Gori P. and Chiarabba C.; 2011: Seismicity and velocity structures along the south-Alpine thrust front of the Venetian Alps (NE Italy). Tectonophysics, 513 , 37-48, doi:10.1016/j.tecto.2011.09.023. Aoudia A., Sarao A., Bukchin B. and Suhadolc P.; 2000: The 1976 Friuli (NE Italy) thrust faulting earthquake: A reappraisal 23 years later. Geophys. Res. Lett., 27 , 573-576. Barba S., Finocchio D., Sikdar E. and Burrato P.; 2013: Modelling the interseismic deformation of a thrust-system: Seismogenic potential of the Souther Alps. Terra Nova, 25 , 221-227, doi:10.1111/ter.12026. Bechtold M., Battaglia M., Tanner D.C. and Zuliani D.; 2009: Constraints on the active tectonics of the Friuli/NW Slovenia area from CGPS measurements and three-dimensional kinematic modelling. J. Geophys. Res., 114 , B03408, doi:10.1029/2008JB005638. Blewitt G.; 2008: Fixed-point theorems of GPS carrier phase ambiguity resolution and their application to massive network processing: Ambizap. J. Geophys. ����� Res., 113 , B12410, doi:10.1029/2008JB005736. Burrato P., Poli M.E., Vannoli P., Zanferrari A., Basili R. and Galadini F.; 2008: Sources of �� ��� ����������� �� Mw 5 earthquakes in northeastern Italy and Western Slovenia: An updated view based on geological and seismological evidence. Tectonophysics, 453 , 157.176. Cattin R. andAvouac J.P.; 2000: Modeling mountain building and the seismic cycle in the Himalaya Nepal. J. Geophys. Res., 105 , 13389-13407. Fig. 3 – Cumulative magnitude-frequencies of the major historical earthquakes of NE Italy (yellow squares) and estimated geodetic moment rates assuming a Gutenberg-Richter distribution, for different fractions (α) of moment being released seismically (a) and for different values of assumed M max (b).